The US Navy and Marine Corps have been engaged in a series of training activities and build-up in the Western Pacific region. Earlier in the month, the 31st Marine Expeditionary Unit staged a series of sequential expeditionary combined-arms operations from the Wasp Amphibious Ready Group ships to shore in the Philippine and East China Seas as well as in the vicinity of Okinawa to show its flexibility in simultaneous multi-island seizures and other operations in a contested littoral environment. More recently, the US Transportation Command staged the “turbo activation” of 28 logistics ships – from a fleet of 87 vessels spread across the Military Sealift Command, Department of Transportation and the Maritime Administration – in the largest mobilisation activity of its kind since Operation Iraqi Freedom in 2003, to test the ability to move heavy equipment overseas in times of conflict. This flurry of activity is a manifestation of long-standing plans and initial training activities that have gradually grown in scope and sophistication. The sequential expeditionary combined-arms exercise formed part of the marines’ efforts to refine the expeditionary advance base operations and the littoral operations in a contested environment concepts, alongside the navy’s work to refine its distributed maritime operations concept. All these efforts are in no small part motivated by what the US defence establishment sees as the growing threat posed by the People’s Liberation Army – notably the expanding missile arsenal – against US forces in the Western Pacific region. The South China Sea constitutes a key area of interest where the “contested littoral environment” is concerned. The US Indo-Pacific Command has been engaging in drills since the beginning of the year to trial its ability to distribute assets, personnel and material across vast swathes of land and waters, in the face of challenges of operating as small units far from the conveniences of a consolidated strike group. Rivalry between China and US plays out in military war games Such demonstrations are timely in signalling American commitment to a sustained military presence in the Western Pacific, focusing on addressing the long-term security challenge posed by a near-peer competitor such as China – when there remains trepidation among regional governments about the growing uncertainties that result from the Sino-US trade friction, simmering tensions in the South China Sea, among others. The element of signalling is more pertinent in view of recent upheavals in the adjacent western neighbourhood of the Western Pacific. Since the recent tanker attacks in the Persian Gulf area, the US has pushed for a 55-ship coalition to secure critical sea lines of communications plying the strategic waterways, but the proposal has at best received a lukewarm response from its traditional allies. Already faced with capacity shortfalls that affect fleet availability for an ever-expanding array of global security commitments, the US Navy in particular may have to bear the primary burden in this proposed maritime coalition. China to show off advanced nuclear weapons in National Day parade Therefore, regional concern about the durability of US security commitment might potentially be amplified following worsening tensions between Iran and the US, especially following the latest Saudi oil attacks, that the Trump administration may have to divert forces from the Western Pacific in the event of an armed conflict. The question would be whether the US military could simultaneously handle two operational fronts that consume scarce resources if such an eventuality arose – a protracted campaign to safeguard the Gulf waterways against the Iranian threat and, say, a conflict in the South China Sea. Notwithstanding, the US government appears keen to demonstrate that extant issues concerning capacity shortfalls will not stymie its wide-ranging and geographically dispersed security commitments. Notably, the “turbo activation” drill came after warnings were raised within the US military about the looming shortfalls of the country’s strategic sealift capacity, which is responsible for moving up to 90 per cent of the army’s and marines’ equipment overseas in times of a major conflict. China unveils supersonic spy drone The army said last year that by 2034, without new investment 70 per cent of the Organic Surge Sealift Fleet would be more than 60 years old, posing an “unacceptable risk in force projection” capability. It also remains plausible that the US military will see an increase in commitments that would strain capacity still further. For example, there are concerns that the marines’ shift to near-peer war fighting would divert its attention from irregular warfare challenges – a problem not just seen in South Asia but also in Southeast Asia, where governments grapple with the persistent threat posed by violent extremism and terrorism. That notwithstanding, the corps recently released the “Commandant’s Planning Guidance” that pushes deeper naval integration, an increase in technologies that are expeditionary, affordable and disposable, emphasising “newer and more affordable over exquisite,” and seeking smaller, lighter, less exquisite but more numerous” warfighting solutions. The US military, therefore, will still have to prepare for a spectrum of low- to high-intensity operations. Finding the right balance through solutions other than embarking on a major build-up – such as the Trump administration’s ambitious plan for a 355-ship navy – or eyeing new bases to disperse forces throughout the region, becomes crucial. Besides promoting inter-service collaboration, such as recent initiatives to rope in the army for multi-domain operations, it becomes necessary to place greater emphasis on US allies and security partners. This approach isn’t new, but in view of the current and future developments, US allies and security partners will play an increasingly indispensable role in sharing the burden of tackling broad-ranging security challenges. It doesn’t help that disputes, like the one between Japan and South Korea , may potentially imperil future cooperation and response to tensions and limited crisis scenarios in the Western Pacific. The onus remains not only on Western Pacific countries to commit towards their national defence and security capacity-building efforts, but also healthy economic and political links with each other. With that it becomes possible for effective collective security in the region, rather than relying solely on the US to save the day. Collin Koh is research fellow at the Institute of Defence and Strategic Studies, a unit of the S. Rajaratnam School of International Studies, Nanyang Technological University, Singapore.